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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2 Apr 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
1.24
Temp.:
20 °C
Remarks on result:
other: Mean of two determinations A and B

Sample measurements, solutions A and B:

Dilution factor

Solution A, concentration,

g/L

Solution A, conductivity,

µS/cm

Solution B,

concentration,

g/L

Solution B, conductivity,

µS/cm

0

5.018

1115

4.290

984

2

2.509

638

2.145

551

4

1.2545

329

1.0725

281.7

8

0.62725

169

0.53625

144.3

16

0.313625

86.2

0.268125

73.8

32

0.1568125

43.8

0.1340625

37.5

64

0.07840625

22.49

0.06703125

19.34

128

0.03920313

11.91

0.03351563

10.33

Solution A:

Concentration solution A, g/L

Concentration solution A,

mol/L

Specific conductivity k,

mS/cm

Equivalent conductivity L,

S cm2/mol

Reciprocal equivalent conductivity 1/L, mol/S cm2

5.018*

0.0130677

1.115

85.3248

0.01171992

2.509

0.0065339

0.638

97.6453

0.01024115

1.2545

0.0032669

0.329

100.7063

0.00992987

0.62725

0.0016335

0.169

103.4611

0.00966546

0.313625

0.0008167

0.0862

105.5426

0.00947485

0.1568125

0.0004084

0.0438

107.2568

0.00932342

0.07840625*

0.0002042

0.02249

110.1463

0.00907883

0.03920313*

0.0001021

0.01191

116.6601

0.00857191

* - concentration neglected for calculations

1/L = a*k + b, slope a = 0.0014831, intercept b = 0.0093514

Ostwald dilution law: Ka = 1/(a*(1/b)2) = 0.059; pKa = - log Ka = 1.23

Solution B:

Concentration solution B, g/L

Concentration solution B,

mol/L

Specific conductivity k, mS/cm

Equivalent conductivity L,

S cm2/mol

Reciprocal equivalent conductivity 1/L, mol/S cm2

4.290*

0.0111719

0.984

88.0783

0.01135353

2.145

0.0055859

0.551

98.6406

0.01013782

1.0725

0.0027930

0.2817

100.8604

0.00991469

0.53625

0.0013965

0.1443

103.3309

0.00967765

0.268125

0.0006982

0.0738

105.6940

0.00946128

0.1340625

0.0003491

0.0375

107.4126

0.0093099

0.06703125*

0.0001746

0.01934

110.7925

0.00902588

0.03351563*

0.0000873

0.01033

118.3543

0.0084492

*- concentration neglected for calculations

1/L = a*k + b, slope a = 0.001531, intercept b = 0.009367

Ostwald dilution law: Ka= 1/(a*(1/b)2) = 0.0573; pKa= - log Ka= 1.24

Average pKa= 1.24.

Description of key information

pKa = 1.24 at 20 °C

Key value for chemical safety assessment

Additional information

The dissociation constant of the substance was determined according to OECD Guideline 112 (conductometric method).